1. Field of the Invention
The present invention relates to a system and method for operating a power supply. More specifically, the present invention relates to a system and method for utilizing battery power sources in an electronic power supply.
2. Background
Conventional electronic power supplies that operate using battery power sources suffer from a number of disadvantages.
For example, a conventional method for providing a DC voltage to a DC-DC converter utilizes two or more batteries in a series configuration. Often, when batteries are configured serially, one battery will become depleted well in advance of the others. This is due, in part, to varying internal series resistances as well as other characteristics that may cause each battery to discharge at a different rate. Where one battery dies in advance of the others in a series configuration, no power can be delivered to the device being powered.
Recharging batteries that are in series can also be problematic. Because the batteries in a stack typically discharge at different rates, the voltage in each battery before recharging will be different. If one of the batteries in series has been severely discharged to the point where gas has started to build on the anode or cathode, that battery can actually reverse polarity. When an attempt is made to recharge the batteries, the battery with a reverse polarity will, in effect, be charged in reverse. This will result in the death of that battery, which means that no power can be delivered to the device being powered as discussed above. Additionally, it has been observed that charging a battery with a reverse polarity can actually cause the battery to be damaged or heat up to the point where it will explode.
Furthermore, when batteries are arranged in series, it is difficult to monitor how much charge is in each of them. Because batteries are manufactured with slight differences, each individual battery will charge and discharge at a different rate. It would be useful to know for discharging and recharging purposes how much charge remains in each battery in a battery pack. In a conventional series arrangement, the overall voltage coming out of a battery pack may be detected, but it is impossible to determine the state of one of the cells in the middle of the stack.
Conventional schemes for operating two or more battery cells in parallel are also disadvantageous in that they require the addition of external parts to add multiple cells to a battery pack, which can be complex and costly. Moreover, conventional techniques for operating cells in parallel do not avoid the problem of over-discharging, or “deep” discharging of a battery that can result in polarity reversal.
A further disadvantage of conventional battery-operated power supplies is that they utilize separate power control chips that must be coupled to the application to be powered using external logic and parts. This makes the design more expensive. Furthermore, because these separate power control chips are not “on chip” with the application being powered, they do not have access to a priori information about impending load changes. Thus, conventional battery-operated power supplies require large load capacitors to act as charge buffers to prevent sudden load changes from pulling a supply voltage out of specification (in the case where a large load is suddenly presented) or from causing the supply voltage to spike too high (in the case where the load current is suddenly turned off).
Conventional battery-operated power supplies also do not monitor the state of batteries by determining how much charge is in them, but instead simply look at the voltage on the battery. Although the voltage on the battery provides an indication of the state of the battery, that information is not as useful as tracking how much charge remains in the battery.
Conventional battery-operated power supplies are also disadvantageous in that they typically utilize a Schottky diode to discharge current into a load. Because a Schottky diode has a typical turn-on voltage of about 0.4 to 0.6 volts, the use of the diode will result in an energy loss equal to the turn-on voltage times the load current. This is lost energy that could have otherwise been used by the load. Where only one or two small batteries are being used, this loss can be quite significant. The use of Schottky diodes is also problematic because it is impossible to control their turn-on and turn-off characteristics beyond their manufactured values.